Virtual auditory displays (including computer games, virtual reality systems or computer music workstations) create virtual worlds in which a virtual listener can hear sounds generated from sound sources within these worlds. In addition to reproducing sound as generated by the source, the computer also processes the source signal to simulate the effects of the virtual environment on the sound emitted by the source. In a computer game, the player hears the sound that he/she would hear if he/she were located in the position of the virtual listener in the virtual world.
One important environmental factor is reverberation, which refers to the reflections of the generated sound which bounce off objects in the environment. Reverberation can be characterized by measurable criteria, such as the reverberation time, which is a measure of the time it takes for the reflections to become imperceptible. Computer generated sounds without reverberation sound dead or dry.
Reverberation processing is well-known in the art and is described in an article by Jot et al. entitled “Analysis and Synthesis of Room Reverberation Based on a Statistical Time-Frequency Model”, presented at the 103rd Convention of the Audio Engineering Society, 60 East 42nd St. N.Y., N.Y., 10165-2520.
As depicted in FIG. 1, a model of reverberation presented in Jot et al. breaks the reverberation effects into discrete time segments. The first signal that reaches the listener is the direct signal which undergoes no reflections. Subsequently, a series of discrete “early” reflections are received during an initial period of the reverberation response. Finally, after a critical time, the “late” reverberation is modeled statistically because of the combination and overlapping of the various reflections. The magnitudes of Reflections_delay and Reverb_delay are typically dependent on the size of the room and on the position of the source and the listener in the room.
FIG. 14 of Jot et al. depicts a reverberation model (Room) that breaks the reverberation process into “early”, “cluster”, and “reverb” phases. In this model, a single feed from the sound source is provided to the Room module. The early module is a delay unit producing several delayed copies of the mono input signal which are used to render the early reflections and feed subsequent stages of the reverberator. A Pan module can be used for directional distribution of the direct sound and the early reflections and for diffuse rendering of the late reverberation decay.
In the system of FIG. 14 of Jot et al. the source signal is fed to early block R1 and a reverb block R3 for reverberation processing and then fed to a pan block to add directionality. Thus, processing multiple source feeds requires implementing blocks R1 and R3 for each source. The implementation of these blocks is computationally costly and thus the total cost can become prohibitive on available processors for more than a few sound sources.
Other systems utilize angular panning of the direct sound and a fraction of the reverberation or sophisticated reverberation algorithms providing individual control of each early reflection in time, intensity, and direction, according to the geometry and physical characteristics of the room boundaries, the position and directivity patterns of the source, and the listening setup.
Research continues in methods to create realistic sounds in virtual reality and gaming environments.